A conventional approach to acquiring high quality iris or face images of moving subjects is to freeze the subject motion by using extremely short exposures. The subject must be brightly illuminated by a flash in order to get a well exposed image. This approach commonly breaks down for larger distances because the flash power that is required in order to obtain an acceptable image often becomes eye unsafe.
Producing a well exposed image without flash illumination typically requires extending the image exposure, which degrades the image quality. One drawback with this approach is extending the image exposure typically introduces motion blur unless the relative motion between the subject and the camera sensor is eliminated.
The motion of a subject relative to the camera sensor can be real, apparent or both. Real motion is the result of the physical motion of the subject and/or the sensor. Real motion is described by a velocity vector, v(t), which gets decomposed into two components. The axial velocity vector points toward the sensor and is aligned with the optical axis of the sensor. The lateral velocity vector is the velocity vector projection into an X-Y plane perpendicular to the optical axis. Axial velocity affects the focusing of camera optics and may introduce magnification blur for long exposures. Lateral velocity causes motion blur.
Existing systems attempt to estimate the velocity vectors and then move items within the camera in order to compensate for axial and lateral motion of the subject relative to the camera. Moveable lenses are widely used as image stabilizing elements in cameras. One known approach is to use a pair of inertial sensors to detect camera relative motion between a subject and the camera and then move the stabilization lens to compensate for the relative motion. An alternative approach employs a tip-tilt minor to compensate for the relative motion.
One drawback with these types of solutions is that they typically cannot track very fast motions. In addition, these approaches usually utilize delicate mechanical parts that make their use problematic in military and security applications.